Fingerprint sensing and matching is a reliable and widely used technique for personal identification or verification. In particular, a common approach to fingerprint identification involves scanning a sample fingerprint or an image thereof and storing the image and/or unique characteristics of the fingerprint image. The characteristics of a sample fingerprint may be compared to information for reference fingerprints already in a database to determine proper identification of a person, such as for verification purposes.
A particularly advantageous approach to fingerprint sensing is disclosed in U.S. Pat. No. 5,953,441 to Setlak. The fingerprint sensor is an integrated circuit sensor that drives the user's finger with an electric field signal and senses the electric field with an array of electric field sensing pixels on the integrated circuit substrate.
Such an electric field fingerprint sensor includes a finger sensing package surrounding the IC substrate and a drive ring carried by the package to drive the user's finger with an electric field signal. Moreover, drive or excitation electronics are typically used in conjunction with the drive electrode. For example, an excitation drive amplifier may be used that drives the finger, via the drive ring, with a signal that may be typically in the range of about 1 KHz to 1 MHz.
A finger sensing IC typically includes additional pins for coupling to the drive ring or drive electrode. Additionally, an additional resistor and a transient voltage suppressor may both be used when coupling a drive ring to the drive circuitry. Still further, in the case of a drive ring, the drive ring may increase the overall size of the finger sensor. In other words, more space is needed for using the drive ring, and thus the overall area of the finger sensor is also increased.